In January of 2004, President Bush outlined a new,
bold vision for U.S. Space Exploration.
The goal of this vision is to help the US improve in scientific, security and economic areas.
As a result, the general public has shown renewed interest in the space program, especially
human exploration. Mankind has often dreamed of traveling into space beyond the moon. It aspires
to fly manned missions to Mars, and hopefully, to the outer planets. This is a goal that began
to see new public interest as a result of the Mars Pathfinder Mission
Mars Pathfinder Mission
and the 1984 discovery in Antarctica of the
Martian meteorite ALH84001,
which hints at the possibility of fossils existing on Mars. In order to accomplish the goals
of human exploration to other bodies, more advanced propulsion technologies need to be further
developed. In support of the Space Exploration Vision, Project Prometheus has been formed to
study the application and flight of a nuclear reactor in space. As a result, Nuclear Thermal
Rockets might be the propulsion we use to fulfill these human exploration dreams.

A Nuclear Thermal Rocket (NTR) creates thrust by heating and expanding a working fluid,
such as hydrogen, a fusion fuel, in a nuclear reactor. An NTR engine has twice the efficiency
of the best chemical engines due to the high energy level produced by the nuclear reactions when
compared to the combustion in chemical thrusters. Consequently, NTR engines have an advantage over
chemical engines when we compare the amount of energy available per unit mass of fuel. Thus,
NTR engines produce
a higher specific impulse (ISP) than current technology chemical rockets. The specific impulse
of a rocket is improved by using a lower molecular weight exhaust. The exhaust of chemical rockets
are constrained by the chemical reaction, but in an NTR, the heat source is not based on the
propellant, so an NTR can use a low molecular weight propellant, such as hydrogen, to improve
performance. The high specific impulse (Isp) levels of an NTR rocket offer opportunities for
missions with shorter trip times and greater payloads that those that can be accomplished using
only chemical propulsion. Keep in mind that this is at the cost of an increased system weight
to accommodate an NTR power plant. An NTR is attractive for many high-energy missions because of
its high thrust to weight ratios of the power plant and engines. NTR propulsion systems are referred
to as high thrust when compared other advanced propulsion systems such as electrical propulsion.
Current advanced NTR propulsion system designs under consideration include straight NTR, Bimodal,
and Tri-modal with LOX augmented thrust. The reactor used in an NTR vehicle operating in the
Bimodal mode, can be used to create electrical power when not being used to produce thrust.
A Tri-modal system includes an afterburner-style operation cycle in which
liquid oxygen (LOX)
is injected into the nozzle for increased thrust (and therefore, lower Isp).
Nuclear Thermal Rocket Propulsion is not a new technology. NTR dates back to the
NERVA program
in the 1960s. The NERVA engine was a solid-core design, which is the traditional and
simplest design to make. Other advanced design concepts include a liquid-core and a gas-core
reactor.

7820 Participation

7820/ Space Mission Design Branch performs Mission and Systems analysis on Nuclear Thermal
Rocket concepts used for missions to Mars, Near Earth Orbiting (NEO) Asteroids and other bodies
within and outside the solar system. With our in-house analysis capabilities, we can apply NTR
system models and optimize ballistic trajectories to Mars and other planetary or sub-planetary
bodies. When system models are unavailable, we develop those elements necessary to model a complete
NTR vehicle. Our work also includes performing mass (e.g. payload) optimization studies for
delivering the heaviest payload possible to Mars or other target body destination. We perform
conceptual design (CAD modeling) and some structural analysis of the NTR spacecraft itself.
We have been and still contribute as integral parts of architecture studies into the application
of NTR propulsion systems to future human and robotic NASA missions.